1. Field of the Invention
The present invention relates to a surface inspection device and method capable of detecting a surface defect in wafer and a CD value variation in line width (or hole diameter) during a semiconductor production process.
2. Description of the Related Art
In recent years, patterns in the semiconductor devices tend to be miniaturized for facilitating the high-speed processing, suppressing the power consumption, and increasing the storage capacity. At the same time, strict managements have also been required for managing the performance of detecting defects occurring in the production process of semiconductor devices, and for managing the line width (to be referred to as “CD” hereinafter; “CD” is the abbreviation for the Critical Dimension). If a surface defect of the wafer or a variation in CD value, which occurs in the exposure process, exceeds an acceptable value, the corresponding wafer or lot is then transferred to a rework process to recover the portion where the problem has occurred, thereby allowing for production of non-defective semiconductor wafers.
For example, when the exposure apparatus has a problem in focal accuracy, an unfavorable change may arise in the cross-sectional shape of the photoresist pattern formed on the wafer surface. Further, with respect to a scanning-type exposure apparatus, diversity in scanning speed may give rise to a fluctuation in exposure amount so as to cause the variation in CD value. As a result, the CD value may go beyond the standard value or a disconnection may be caused after etching. Since the problematic phenomena are compositive, if they cannot be discovered early to solve the problems in time, a large number of lots may become defective, thereby bringing about a great loss.
Therefore, the defect detection and the CD value management performed right after the exposure process are very important. A method for detecting defects is considerably effective for a device for automatically inspecting defects. In this method, an illumination light is irradiated on the semiconductor wafer, the diffracted lights from the repetition pattern on the wafer is received, and the defects are detected based on the fact that the amount of diffracted lights from a defect changes because of the variation in CD value at the defect. The devices adopting the method have been in practical use (see Japanese Patent Application Laid-Open No. 2006-105951, for example). Because such defect inspection devices, which are referred to as macroscopic inspection devices, have a high throughput due to the collective imaging of the entire surface of a wafer, they play a very important role in the production lines. However, in consideration of the property of the devices, there are limitations in the high-resolution inspection for microscopic regions and the quantitative output of the amount of CD value variation.
On the other hand, as a device for managing the CD value, there is an electron microscope device called CD-SEM (Critical-Dimension Scanning Electron Microscope; also called length-measuring SEM). The CD-SEM is configured to measure the line width of line and space (to be referred to as L&S hereinafter), and the diameter of contact holes (to be referred to as C/H hereinafter) or the interval with an adjacent C/H, by using an electron beam, and is configured to output the measurement result as the CD value. Thereby, it is possible to quantitatively determine whether or not the CD value is within the standard. In this manner, although the CD-SEM plays an important role as a measuring apparatus, it is difficult to measure the entire surface of a wafer, because it needs approximately five seconds of time to measure one point. Therefore, under the circumstances, the wafers are measured and managed by the sampling inspection in which one piece of wafer per lot is picked out to perform the inspection for only a few shots within the wafer surface, and for only a few points in each shot.